In a gas turbine engine, hot combustion gases generally flow from one or more combustors through a transition piece and along a hot gas path. A number of turbine stages typically may be disposed in series along the hot gas path so that the combustion gases flow through first-stage nozzles and buckets and subsequently through nozzles and buckets of later stages of the turbine. In this manner, the nozzles may direct the combustion gases toward the respective buckets, causing the buckets to rotate and drive a load, such as an electrical generator and the like. The combustion gases may be contained by circumferential shrouds surrounding the buckets, which also may aid in directing the combustion gases along the hot gas path. In this manner, the turbine nozzles, buckets, and shrouds may be subjected to high temperatures resulting from the combustion gases flowing along the hot gas path, which may result in the formation of hot spots and high thermal stresses in these components. Because the efficiency of a gas turbine engine is dependent on its operating temperatures, there is an ongoing demand for components positioned within and along the hot gas path, such as turbine nozzles, buckets, and shrouds, to be capable of withstanding increasingly higher temperatures without deterioration, failure, or decrease in useful life.
Certain turbine nozzles, particularly those of middle and later turbine stages, may include a one or more passages or cavities defined within the nozzles for cooling purposes. For example, cooling passages may be defined within the inner platform, the outer platform, and/or the vane of a turbine nozzle, depending on the specific cooling needs of the nozzle, as may vary from stage to stage of the turbine. According to certain configurations, the cooling passages may be defined near a hot gas path surface of the turbine nozzle. In this manner, the cooling passages may transport a cooling fluid, such as compressor bleed air, through the turbine nozzle for exchanging heat in order to maintain the temperature of the region near the hot gas path surface within an acceptable range. Based on a desire to maximize the region of cooling coverage, the cooling passages may be long and may have a complex shape, such as a winding or serpentine shape, including a number of turns or bends. Long cooling passages having a complex shape, however, may be challenging and costly to manufacture, and also may result in an undesirable pressure drop along the cooling passages. Moreover, the heat transfer performance of such cooling passages may vary significantly, and thus optimizing the cooling passages for the applicable turbine stage may be particularly challenging.
There is thus a desire for an improved turbine nozzle including a cooling passage configuration for cooling the turbine nozzle at high operating temperatures. Specifically, such a cooling passage configuration should maximize the region of cooling coverage while minimizing the length and complexity of the cooling passages. In this manner, such a cooling passage configuration should minimize the cost and complexity of manufacturing the turbine nozzle, and also should minimize the pressure drop along the cooling passages. Moreover, such a cooling passage configuration should minimize variation of the heat transfer performance of the cooling passages, and thus should ease optimization of the cooling passages for the applicable turbine stage.